Methods of stretching DNA are described in K H Rasmussen, R Marie, J M Lange, W E Svendsen, AKristensen, and K U Mir, Lab chip, 2011, 11:1431-44 and A device for extraction, manipulation and stretching of DNA from single human chromosomes; D L V Bauer, R Marie, K H Rasmussen, A Kristensen, K U Mir, 2012 Nucl Acids Res, 2012, 1-7, DNA catenation maintains structure of human metaphase chromosomes. However, additional methods of elongating DNA are desirable.